25556561 has 2 divisors, whose sum is σ = 25556562. Its totient is φ = 25556560.

The previous prime is 25556549. The next prime is 25556563. The reversal of 25556561 is 16565552.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 22515025 + 3041536 = 4745^2 + 1744^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-25556561 is a prime.

Together with 25556563, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (25556563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 12778280 + 12778281.

It is an arithmetic number, because the mean of its divisors is an integer number (12778281).

Almost surely, 2^25556561 is an apocalyptic number.

It is an amenable number.

25556561 is a deficient number, since it is larger than the sum of its proper divisors (1).

25556561 is an equidigital number, since it uses as much as digits as its factorization.

25556561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 45000, while the sum is 35.

The square root of 25556561 is about 5055.3497406213. The cubic root of 25556561 is about 294.5557269277. Note that the first 3 decimals are identical.

The spelling of 25556561 in words is "twenty-five million, five hundred fifty-six thousand, five hundred sixty-one".